This invention relates to a barometer for measuring gas pressure around a quartz oscillator using the quartz oscillator.
There is an urgent need in industrial applications to measure continuously gas pressure ranging from ambient pressure to 10.sup.-3 Torr with a single sensor.
A quartz barometer which utilizes the phenomenon that the frequency at resonance of a quartz oscillator increases with a decreasing gas pressure surrounding the oscillator satisfies to some extent the industrial requirement described above. However, this barometer involves a critical problem in that the lower limit of measurement is about 10 Torr. Though a heat conduction vacuum gauge such as the Pirani gauge has a lower limit value of measurement of about 10.sup.-4 to 10.sup.-3 Torr, it is not free from the same problem as that of the quartz type barometer because its upper limit of measurement is about 10 Torr.
It has been shown recently that the resonance resistance of a quartz oscillator depends upon ambient gas pressure over an extremely wide range, and that a barometer which can continuously measure pressure ranging from ambient atmospheric pressure to 10.sup.-3 Torr can be realized by utilizing this property. This is reported, for example, in "Development of Ultra-Miniature Vacuum Sensor Using Quartz Oscillator" in the magazine "Instrumentation", 1984, Vol. 27, No. 7.
However, in a quartz barometer having the prior art construction which utilizes the temperature depedence of the resistance of a quartz oscillator at resonance described above, a problem has been left unsolved in that precision measurement can not be readily effected because the resistance of the quartz oscillator at resonance varies markedly with temperature, particularly in the low pressure range of roughly 10.sup.-3 to 10.sup.-2 Torr.